The Northern Ireland Cohort for the Longitudinal Study of Ageing (NICOLA) is an opportunity to conduct methodology research relevant to many features of a large prospective study. NICOLA will begin in earnest in Northern Ireland in 2013 and is being conducted by a multidisciplinary team in the Centre for Public Health at Queen's University Belfast. It is an omnibus programme of research on ageing that will continue for at least 10 years and will recruit 8500 middle-aged people in Northern Ireland and follow them into old age, providing a comprehensive assessment of their physical and mental health, their lifestyles, and their social and economic decision making. NICOLA will look at how they perceive disability and health, and how this differs between well-off and disadvantaged groups. NICOLA will also study various genetic, biological and psychological factors, including how participants perceive risk and value their time, and the effect of this on their retirement behaviour (including how they manage their money and their health). People over the age of 50 will be invited to take part and asked to complete detailed interviews and questionnaires every 2 years and health assessments every 4 years.